Engineers typically design high-pressure oil field plunger pumps in two sections; the (proximal) power section and the (distal) fluid section which are connected by multiple stayrods. In the fracturing industry and hereafter in this application these sections are referred to as the power end and the fluid end. The power end, illustrated in FIG. 1, usually comprises a crankshaft, reduction gears, bearings, connecting rods, crossheads, crosshead extension rods, etc. Commonly used fluid ends usually comprise a plunger pump housing having a suction valve in a suction valve bore, a discharge valve in a discharge valve bore, an access bore, and a plunger in a plunger bore, plus high-pressure seals, retainers, etc. FIG. 1 illustrates a typical fluid end showing its connection to a power end by stay rods. A plurality of plungers similar to that illustrated in FIG. 2A may be combined, as suggested in the Quini-plex or five plunger fluid end housing illustrated in FIGS. 2A and 3B. Fluid ends also include a suction manifold to supply fluid to the suction valve bore, suction seat, and suction valve. The suction manifold is typically attached to the fluid end by bolts. The suction manifold is typically connected to an external suction feed hose used to supply fluid to the manifold by a tubular connection on either end of the suction manifold. The discharge manifold which allows for the exit of the pumped high pressure fluid is usually integral to the fluid end.
Valve terminology varies according to the industry (e.g., pipeline or oil field service) in which the valve is used. In some applications, the term “valve” means just the valve body, which reversibly seals against the valve seat. In other applications, the term “valve” includes components in addition to the valve body, such as the valve seat and the housing that contains the valve body and valve seat. A valve as described herein comprises a valve body and a corresponding valve seat, the valve body typically incorporating an elastomeric seal within a peripheral seal retention groove.
Valves can be mounted in the fluid end of a high-pressure pump incorporating positive displacement pistons or plungers in plunger bores. Such valves typically experience high pressures and repetitive impact loading of the valve body and valve seat. These severe operating conditions have in the past often resulted in leakage and/or premature valve failure due to metal wear and fatigue. In overcoming such failure modes, special attention is focused on valve sealing surfaces (contact areas) where the valve body contacts the valve seat intermittently for reversibly blocking fluid flow through a valve.
Valve sealing surfaces are subject to exceptionally harsh conditions in exploring and drilling for oil and gas, as well as in their production. For example, producers often must resort to “enhanced recovery” methods to insure that an oil well is producing at a rate that is profitable. And one of the most common methods of enhancing recovery from an oil well is known as fracturing. During fracturing, cracks are created in the rock of an oil bearing formation by application of high hydraulic pressure. Immediately following fracturing, a slurry comprising sand and/or other particulate material is pumped into the cracks under high pressure so they will remain propped open after hydraulic pressure is released from the well. With the cracks thus held open, the flow of oil through the rock formation toward the well is usually increased.
The industry term for particulate material in the slurry used to prop open the cracks created by fracturing is the proppant. And in cases of very high pressures within a rock formation, proppant may comprise extremely small aluminum oxide spheres instead of sand. Aluminum oxide spheres may be preferred because their spherical shape gives them higher compressive strength than angular sand grains. Such high compressive strength is needed to withstand pressures tending to close cracks that were opened by fracturing. Unfortunately, both sand and aluminum oxide slurries are very abrasive, typically causing rapid wear of many component parts in the positive displacement plunger pumps through which they flow. Accelerated wear is particularly noticeable in plunger seals and in the suction (i.e., intake) and discharge valves of these pumps.
Back pressure tends to close each individual valve sequentially when downstream pressure exceeds upstream pressure. For example, back pressure is present on the suction valve during the pump plunger's pressure stroke (i.e., when internal pump pressure becomes higher than the pressure of the intake slurry stream. During each pressure stroke, when the intake slurry stream is thus blocked by a closed suction valve, internal pump pressure rises and slurry is discharged from the pump through a discharge valve. For a discharge valve, back pressure tending to close the valve arises whenever downstream pressure in the slurry stream (which remains relatively high) becomes greater than internal pump pressure (which is briefly reduced each time the pump plunger is withdrawn as more slurry is sucked into the pump through the open suction valve).
The suction manifold plays a vital role in the smooth operation of the pump and valve performance and life. All fluid entering the pump passes through the suction manifold. If the suction manifold is poorly designed, incomplete filling of the plunger bore may result, which in turn leads to valves closing well after the end of the suction stroke, which in turn results in higher valve impact loads. High valve impact loads in turn result in high stress in the fluid end housing and ultimate premature failure of the valves, seats, and/or housing.
To insure complete filling of the plunger bore requires fluid energy in the suction manifold and fluid energy in the plunger bore during the suction stroke. The pumped fluid typically acquires fluid energy from the fluid pressure from a small supercharging pump immediately upstream from the pump of this invention. The fluid energy can be dissipated by turbulence or friction within the suction filling plumbing or line and in the suction manifold. Thus the design of the suction manifold is critical to maintaining fluid energy. Fracturing pumps typically pump a very heavy and viscous fluid as the fluid is composed of heavy sand suspended in a gel type fluid. With this type of fluid it is very easy to lose fluid energy to friction and/or turbulence.
A traditional design Suction Manifold is illustrated in FIGS. 2A and 2B. The fluid end sectional view of FIG. 2B is defined in FIG. 2A. An alternate sectional view at a right angle to the sectional view of FIG. 2B is illustrated in FIG. 3B; this sectional view is defined in FIG. 3A. Sharp corners at the intersection of the horizontal main chamber and the vertical suction valve feed ducts result in turbulence and loss of fluid energy.
Zoomie style suction manifolds illustrated in FIGS. 4 and 5, have gained some acceptance in the industry. By intuition, it is incorrectly assumed that the long sweep ell style ducts reduce turbulence and that the flow in the manifold is uni-directional. However because each suction valve opens and closes at different intervals, flow is actually interrupted when the valve is closed. Furthermore flow is reversed momentarily as the valve closes. When flow reverses, turbulence is generated at the sharp corner positioned at the intersection of the main suction manifold chamber and the ell that functions as a duct for feeding the corresponding suction valve. When the flow stops in a portion of the manifold, some fluid energy is lost and fluid energy is expended to resume flow when the suction valve opens. In addition there is considerable frictional loss in the long sweep ell ducts that the pumped fluid must travel through resulting in even greater loss of fluid energy within the Zoomie style suction manifold.
All the previously discussed manifolds, FIGS. 1-5, plus the manifold of the reference application Ser. No. 14/078,366, lose fluid energy because of the frictional loss and turbulence due to the distance that the fluid must travel from the external connection, previously referred to as the tubular connection, is located at either end of the suction manifold. Thus there is greater frictional loss of fluid energy in the ducts located at the farthest distance from the external connection. This loss of fluid energy can result in incomplete filling of the plunger bore farthermost from the suction manifold external connection, which can result is impact loading of the valve against the seat as previously discussed.
Ideally, the external connection to a pump suction manifold would be centrally located on the manifold in order to reduce the fluid travel and friction loss at each manifold port. The location of the external connection at either end of the suction manifold is usually, dictated by the mounting of these high-pressure plunger-type pumps on the tractor truck trailers necessary for these pumps to be moved from one oilwell location to another location after each and every fracturing operation. These trailers are usually parked side-by-side on a job site because of the limited available space for all the equipment necessary to successfully fracture an oilwell. All of these factors combine to influence the location of the external connection of manifolds of the prior art because of limited space between the bottom of the suction manifold and the deck of the trailer. Additionally, the tight parking at the job site may result in complications including tight, restricting bends in the external suction feed hose used to supply fluid to the suction manifold through the external intake connection, particularity if a centrally located external connection is positioned at a right angle to the manifold chamber.
Thus, by default, suction manifolds of the prior art for oilfield high-pressure plunger-type pumps on tractor truck trailers are designed with external connections at either end of the manifolds. However, for oilfield mud pumps which are skid mounted (rather than truck mounted) without space limitations, center feed external intake connections on the suction manifolds are somewhat common as shown in FIGS. 6A&B and FIGS. 7A, B, C, & D. The suction manifold of FIGS. 6A&B is an improved design with smooth slow bends that minimize fluid energy loss. Unfortunately these manifolds can only be manufactured from steel castings. Manifold castings require separate patterns for each individual pump models because the various and many pump models have different configurations including but not limited to the number of plungers (usually 3-5 plungers) and various spacing that include 8, 9, 10, 10.5 & 12 inch spacing between the plungers. Therefore, tooling and raw material inventory to satisfy each and every configuration is extensive and expensive.
FIGS. 7A-D illustrate a mud pump model similar to the previously illustrated model in FIGS. 6A&B. The external connection of the latter manifold is also centrally located on the manifold, however this manifold is constructed by welding together various pieces of pipe. FIGS. 7C&D illustrate turbulence and fiction loss with this design due to the sharp corners at the welded pipe connections. As such, the suction manifold of FIGS. 7A-D offers limited improvement in performance as compared with the manifolds of the prior art in FIGS. 1-5. Neither of the suction manifolds illustrated in FIGS. 6A&B or 7A&B are suitable for utilization with high-pressure plunger-type pumps mounted on tractor trailers such as fracturing trucks because of space limitations.
Ideally, the centerline of a center feed external intake connection on a suction manifold would be aligned and parallel with the centerline of the center-most suction bore of the fluid end housing. When the centerlines are aligned the flow is uninterrupted by changes in direction of the fluid flow eliminating any loss of fluid energy in the fluid. However for fracturing pumps mounted on trucks, the close proximity of the truck bed restricts such alignment because the limited space with such an alignment would result in kinks or sharp bends in the suction feed hose and further loss of fluid energy.